1. Field of the Invention
The present invention relates to a plate-like workpiece holder used for a wire electric discharge machine when stacked workpieces are machined to reduce machining time per workpiece.
2. Description of the Related Art
When a plurality of plate-like workpieces are machined by a wire electric discharge machine, if the plurality of plate-like workpieces stacked are machined, the machining time per workpiece can be reduced. However, when the plurality of workpieces stacked are secured, the machining time or machining precision may be adversely affected depending on the method of securing the plurality of workpieces. Accordingly, the plurality of workpieces need to be secured to prevent a generation of space between workpieces that causes a wire break during wire electric discharge machining or reduction in the machining precision. For example, Japanese Patent Application Laid-Open No. 6-47625 discloses a securing tool for stack cutting that secures, in a tightening manner, upper and lower metal plates to a machining workpiece stage with a plurality of securing bolts.
A force to hold stacked plate-like workpieces is applied only in a vertical direction (Z-axis direction). However, there is no force that holds these stacked plate-like workpieces in a horizontal direction (X-axis direction) or an anteroposterior direction (Y-axis direction), so the stacked workpieces deviate. If the stacked plate-like workpieces are held in the horizontal direction (X-axis direction) or the anteroposterior direction (Y-axis direction), the stacked plate-like workpieces are deformed by the holding force and the space between the stacked plate-like workpieces is generated, thereby causing a wire break as described above. In addition, a wire electric discharge machine cannot be used until the plurality of plate-like workpieces are secured to the wire electric discharge machine, so the availability rate of the wire electric discharge machine is reduced.
The securing tool for stack cutting disclosed in the above Japanese Patent Application Laid-Open No. 6-47625 secures the upper and lower metals plates to the machining workpiece stage using the plurality of securing bolts, so the tightening force is unlikely to become even in some places, a space is generated between stacked upper and lower metal sheets, the speed of electric discharge machining is different between the stacked upper and lower metal sheets, or the tightening force of securing bolts becomes uneven as the cutting position in an object to be machined advances during electric discharge machining by the wire electrode.